Commercial use of “privacy” window in automobiles and/or architectural applications has become more popular over the years. Such glasses are sometimes formed from a standard soda-lime-silica glass composition to which is added various colorants designed to achieve desired color and spectral properties. Desired spectral properties include low visible light transmission, low infrared (IR) transmission, and/or low ultraviolet (UV) transmission, with these terms being defined as follows:
Lta as visible light transmission,
UV as ultraviolet light transmission, and
IR as infrared light transmission.
One conventional privacy glass is known as “Venus 10.” Venus 10 is believed to have the following colorant portion and spectral characteristics at a thickness of about 4 mm:
INGREDIENT/SPECTRALAMOUNT/VALUEtotal iron: 2.693% (wt. %)cobalt oxide:0.0277% (wt. %)chromium oxide:0.0012% (wt. %)Lta10.24%% UV1.35%% IR1.76% FeO0.9243Dom. λ490Ex. Purity, %22.07L* (D65)40.57a*−15.6b*−4.49
While Venus 10 has good color and visible/IR transmission characteristics, it is problematic in that it requires too much total iron (total iron herein is referred to as Fe2O3), namely about 2.693%. This high amount of total iron is undesirable in that it typically requires a special shallow tank to be used for melting the same (a high amount of total iron is difficult to efficiently melt during the process of glass manufacture on a consistent basis).
In view of the above, it is apparent that there exists a need in the art for a new glass composition and/or method of making the same which enables low visible and/or IR transmission characteristics to be achieved without needing an undesirably large amount of total iron.
U.S. Pat. No. Re 37,328 to Pecoraro et al. discloses an IR absorbing glass including iron and cerium in certain examples. Unfortunately, the glass of the '328 patent has a much too high visible transmission of at least about 64%.
U.S. Pat. No. 5,411,922 to Jones discloses a neutral gray-green low transmittance glass which includes iron, cobalt, selenium and titanium. Unfortunately, the example glasses of the '922 patent have a rather high IR transmission.
U.S. Pat. No. 6,413,893 to Shelestak discloses a green privacy glass including iron, chromium, cobalt, selenium and titanium. Unfortunately, most examples glass of the '893 patent require large amounts of chromium (e.g., Cr2O3). For instance, example nos. 1-85 of the '893 patent require at least 0.0210% Cr2O3. Such large amounts of chromium are often undesirable because Cr defects can result in the final glass product. Meanwhile, in examples of the '893 patent where lower amounts of chromium are used, the glass is problematic in that IR transmission is too high (e.g., see example nos. 86, 89, 194, 195 and 255).
U.S. Pat. No. 5,023,210 discloses a low transmittance grey glass including iron, chromium, selenium and cobalt. Again, the glass of the '210 patent is problematic in that too much Cr is used, which is undesirable for the reasons discussed above.
In view of the above, it is apparent that there exists a need in the art for a new glass composition which overcomes the above problems while achieving low visible and/or IR transmission properties.